The present invention relates to deep well drilling and, more particularly, to drill collars forming a part of a rotary drill string.
In gas and oil well drilling operations employing the rotary drilling method, it is customary to include one or more drill collars in the drill string above the drill bit. Drill collars are rather heavy rigid members which lend weight and rigidity to the drill string to increase the penetration rate and resist misdirection of the bit axis, thereby tending to maintain a proper vertical direction of travel of the bit.
The collars are tubular to permit downward passage of drilling fluid or mud from the surface, through the string, and through the drill bit into the annulus. The drilling fluid is pumped through the drill collars and drill bit and into the annulus, whereupon it is conducted upwardly to the surface. The drilling fluid serves to seal-off porous zones, flush-out cuttings, and lubricate and cool the drill bit. Problems have heretofore been experienced as the result of excessive drill fluid pressures at the drill bit, which pressures have been relieved by the provision of jets in the drill collars which discharge drilling fluid above the drill bit. As a result, hydrostatic pressure below the jets is reduced and an upward lift is imparted above the bit to the returning fluid. Examples of such jets may be found in U.S. Pat. Nos. 2,765,146 and 2,805,043 issued to Williams, Jr. on Oct. 2, 1956 and Sept. 3, 1957, respectively, and in U.S. Pat. No. 3,908,771 issued to the present inventor on Sept. 30, 1975.
In the disclosed drill collar of U.S. Pat. No. 3,908,771 a plurality of passages are formed completely through the drill collar to define discharge outlets for drilling mud. A nozzle communicates an axial through-bore of the drill collar with the mid-point of the passages, whereupon equal and opposite flows of drilling fluid are discharged from the ends of each passage. While such an arrangement can perform adequately, room for improvement remains.
It is, therefore, an object of the present invention to provide an improved drill collar over that disclosed in U.S. Pat. No. 3,908,771.
It is a further object of the invention to promote fluid uplift in the annulus in a manner assisting rotation of said collar.
It is an additional object of the invention to promote fluid uplift in the annulus in a manner tending to maintain the drill collar vertically oriented.
It is still another object of the invention to discharge drilling mud through the drill collar above the cutter bit in a manner maintaining the discharge passages in an unclogged condition.